1. Field of the Invention
The invention relates to a semiconductor memory device such as a NAND-type flash memory, and more particularly, relates to a flexible clock scheme used in the semiconductor memory device.
2. Description of Related Art
A flash memory is usually used as a memory medium for mobile equipments such as portable multifunction terminals (smart phones), tablet terminals and the like. In response to requirements for the mobile equipments in terms of low power consumption, the flash memory is also required to achieve low power consumption.
A flash memory disclosed in Patent Document 1 is capable of monitoring a power voltage came from the outside, and reducing a clock frequency for operating a charge pump in order to reduce power consumption when detecting that the power voltage is lower than a specific level. Further, a flash memory disclosed in Patent Document 2 is capable of stopping a clock of a state machine, which does not require a long period of operation, when operations such as erasing operations are performed for memory cells, such that power consumption may be further reduced.